Goal:To employ external magnetic fields to controllably position and orient magnetic micro-robots. We demonstrate this approach in the 2007, 2008, and 2010 NIST Microrobotics Challenges.

Approach:Six electromagnetic coils surround a working volume, wherein the magnetic micro-robot (Mag-μBot) resides. The four upright coils create in-plane magnetic fields and gradients, while the top and bottom coils create vertical fields and gradients. Using DC in-plane fields and gradients alone cannot reliably translate a Mag-μBot, due to high stiction and friction to the surface. A nonuniform oscillating magnetic field is produced, which causes the Mag-μBot to experience a nonuniform rocking motion. This induces stick-slip behavior in the robot resulting in controllable translation. By varying the pulsing frequency and waveform shape, control of micro-robot velocity is achieved. Maximum velocities observed are typically over 50 mm/s in air (over 100 body lengths per second) and 20 mm/s underwater.
A Mag-μBot is a composite of Neodymium-Iron-Boron particles in a polyurethane matrix, which is fabricated in a photolithography-based molding procedure to create large numbers of Mag-μBots. They can be fabricated to arbitrary planar shapes, with dimensions typically under 500 μm. Alternatively, a piece of bulk Neodymium-Iron-Boron can be laser cut into a micro-robot in a serial fashion.
Visual servoing is possible using computer vision to track the Mag-μBot. Motion tasks can be planned and executed using path-planning techniques from a computer. Autonomous strategies can be applied to position and orient microparticles in the workspace.

Multi Micro-Robot ControlAlthough the control magnetic fields cannot be focused to a point to control multiple micro-robots independently, there are several ways to achieve independent control.
Multiple Mag-μBots can be operated with the use of specialized surface capable of creating local electrostatic fields, which selectively lock down (anchor) Mag-μBots. Anchored micro-robots do not move in the presenece of a driving magnetic field, but unanchored micro-robots do. This allows for the serial uncoupled positioning of multiple Mag-μBots, or the parallel symmetric motion of multiple Mag-μBots.
Alternatively, multiple Mag-μBots can be made with different properties, to respond differently to the input fields. By learning the response of the micro-robots to different actuation waveforms, the computer can automatically calculate which fields to apply to get multiple micro-robots to move to arbitrary goal positions.

Benefits:Externally controlled magnetic actuation for micro-scale robots benefits from the ability of operation on arbitrary surfaces. Most surfaces are feasible, provided that they are not magnetically active and not overly sticky. Examples of valid surfaces are glass, silicon, hard plastics, and machined aluminum. In comparison, approaches such as electrostatic actuation for micro-robots requires a specialized surface with electrodes. Without these constraints, Mag-μBot motion on arbitrary surfaces can be realized, as actuation is independent of the surface.
In addition the Mag-μBot can operate in a fluid environment, provided the fluid is not too viscous such that it impedes the micro-robot's motion. In experiment, fluids up to 50 cSt in viscosities can be used, however the micro-robot experiences velocity reductions due to fluid damping. Fluid environments are advantageous as micro-scale stiction forces are reduced, which improves the reliability of micro-scale manipulation tasks.
As the Mag-μBot is simply a permanent magnet, it is not fragile and is physically robust, capable of being handled in harsh environments. Susceptibility to dirt, contamination, and humidity fluctuations are minimal with this design, when compared to other micro-robot approaches.

Videos: (newest to oldest)

A teleoperated star-shaped Mag-μBot inserting a peg into a gap (2010) [YouTube video]